The present invention relates to improvements of half-wave rectifying circuits for use in electric instrumentation, synchronous detection circuits, and similar applications.
Previously, half-wave rectification of alternating voltage signals has been accomplished, for example, by a diode or other rectifying or differential conducting means connected between a source of alternating voltage signals and a load, the common terminals of source and load being connected together. Depending on the polarity of the diode connection, the output voltage was positive or negative and the error in output voltage was the voltage drop of the rectifying means itself.
Numerous attempts have been made to reduce or eliminate the error of the rectifying means. For example, mechanical switches operated by a source of alternating current and synchronized to the source of alternating voltage signals have been used with some success, although limitations of contact life and restricted speed of response to the synchronizing signals have restricted applications to power circuits as opposed to measurement applications.
In signal detecting applications, field-effect transistors have been used such as described in my U.S. Pat. No. 3,662,113 entitled STEREOPHONIC DEMODULATOR APPARATUS AND AUTOMATIC MONOPHONIC-STEREOPHONIC SWITCHING CIRCUIT and dated May 9, 1972. Here, the signal voltage has to be kept small with respect to the pinch-off voltage of the field-effect transistor and the load resistance has to be kept large with respect to the channel resistance of the field-effect transistor in its "on" state. Consequently, maximum output current is limited to values typically not exceeding a few tens of microamperes, and the switching or synchronizing signal may require neutralization of undesirable capacitive coupling to the signal circuit.
In other signal detecting applications use has been made of a high-gain amplifier having an "inverting" input where the input signal is coupled to the amplifier input via a series resistor and the rectified output is obtained via a diode connected to the output of the amplifier. A feedback resistor connected between the rectified output terminal and the amplifier output determines the gain of this circuit, while a second diode connected between amplifier output and amplifier input, opposite in polarity to the first diode, prevents amplifier overload for signals of "reverse" polarity.
Such a circuit requires typically two well regulated power supply voltages of opposite polarity for operation of the inverting amplifier, adding considerably to the complexity of this circuit.
In the present invention it has been discovered that a half-wave rectifier circuit can be constructed employing a high-gain differential amplifier operated from a single power supply without need of voltage regulation and thereby obviating the two well regulated power supplies required in prior art. Furthermore, the two diodes required in prior art are no longer required, thereby eliminating a source of dependence of such rectifier circuits on temperature.
Accordingly, an object of the present invention is to provide an improved half-wave rectifying circuit.
Another object of the present invention is to provide a half-wave rectifying circuit with minimal error.
Another object of the present invention is to provide an improved half-wave rectifier employing a high-gain differential amplifier using only a single power supply without need for voltage regulation.
Another object of the present invention is to provide an improved half-wave rectifier which is independent of temperature.
Other and further objects of the invention will be obvious upon an understanding of the illustrative embodiment about to be described or will be indicated in the appended claims, and various advantages not referred to herein will occur to one skilled in the art upon employment of the invention in practice.